Submarines -- the ultimate toy for the super rich

When director James Cameron descended to the bottom of the Pacific on Monday, he not only shed light on the world's deepest ocean, but the world's most exclusive hobby: private submarine voyages.

The phenomenally profitable director of "Avatar" piloted an ungainly looking, bright green, one-seat sub to an amazing 36,000 feet, or 11,000 meters, down into the Mariana Trench.

Only the third person to go there, Cameron led the mission, which was entirely privately funded.

Meanwhile, on the other side of the globe, another mega-rich man with a sub, Richard Branson, is plotting to penetrate the Atlantic's deepest point, the Puerto Rico Trench.

For a man who's done extreme sailing and hot air ballooning, a jaunt miles under the ocean in a James Bond-style, winged mini-sub is the logical next step. He dreams of finding "Spanish galleons" or "a species that hasn't been discovered."

"It's enormously exciting that the oceans can now be explored and we have the vehicles to do that," Branson told AFP from his private Necker Island in the Caribbean.

Charles Kohnen, co-founder of submarine builders SEAmagine, said private sub owners are still a tiny group -- perhaps less than a dozen individuals -- but that the general trend of ever fancier toys for billionaires is likely to change that.

Most underwater craft on the civilian market are technically called submersibles, meaning they have only limited autonomy and need yachts to act as motherships. True submarines are more closely related to the naval equivalents, although both types can make safe journeys to at least 500 feet (150 meters), and in most cases a great deal further.

When SEAmagine started 16 years ago, "yachts weren't big enough to hold submarines. The evolution we've seen over the last five, seven years is interest from the private sector and it's directly related to the yachts, the mega-yacht industry," Kohnen said.

One recent private client has a specially designed 82 foot (25 meter) catamaran with a helicopter deck and submersible launch. Another didn't need any particular design changes to hold his submersible, but that's only because he has a 280 foot (85 meter) "luxury ship."

"A submarine -- it's not just a jet ski," Kohnen said.

His craft retail at between $1 million and $3 million. But the annual upkeep of $15,000-$20,000 is practically spare change to the super rich and a fraction of what it costs to fly an executive jet.

A company called US Submarines targets an even further frontier, offering luxury subs in addition to the more common submersibles.

Business is growing in the smaller craft sphere, especially "from the scientific community and very much more from the film community," Marc Deppe, an executive with subsidiary Triton Submarines, told AFP.

What they'd like to find now, Deppe said, is the world's first private owner of a full-blown submarine -- a modern day Captain Nemo.

US Submarines offers the "Nomad," described as having an interior equivalent to a personal jet plane, the "Seattle," comparable in comfort to a large yacht, and the amazing "Phoenix."

This vessel, a full 213 feet (65 meters) long, would be able to cross an ocean, diving whenever weather got rough, and has so much room it would carry its own mini-sub.

At $78 million, according to its website, the "Phoenix" exists only on paper, but could be built as soon as a buyer ordered. "It's going to take someone who's a little bit extravagant, who has a passion to be the first one to have that type vessel," Deppe said.

Kohnen said subs are still too daunting a prospect for most wealthy people, but that those who take the plunge will find a magical world on the other side of their bubble windows.

"How little we know is astounding. There's much to be discovered," Kohnen said. "We take photos and bring it to universities and they scratch their heads and say 'what is that?' What you see out there doesn't look real. It's amazing."